1 Transistor FM Spybug

Introduction: 1 Transistor FM Spybug

In this instructable i will show you how you can make the simplest spybug ever! I was looking for a project to make for fun when i found this FM transmitter,quickly i got curious, it is a simple FM transmitter but can it become even more simpler? The answer is yes! I replaced the variable capacitor with a fixed one, re-calculated the tank circuit (LC circuit) to be able to tune it only by the coil instead of the variable capacitor.

PS: this circuit design is unstable, the resonant frequency drifts off if you get your hands close to the antenna or the circuit, the length of the antenna affects the resonant frequency, but it still a fun project to make.

If you can clamp down the spring end to the transmitter into a frame and the other end to a mechanical adjuster, one can adjust the frequency like one of those old Health Kit Ham radios. A spring is perfect for an FM transmitter. For improved range, a 5/8 length antenna would really help. Copper or aluminum would be best for the spring being an antenna. Steel would work alright, but not for the small transmitter. Nice to see your instructions have a copper alloy spring. Years ago, I picked up one of those spy like camera and mic ink pens. It charges the battery via USB. It will hold a total of 3 30 second movies at low 640 resolution. It's more of a gimmick device. Nice to see your work for the mic in a FM transmitter.

This design is good for understanding how fm transmitters work, not so great fo actual trnsmitting. I built it and like said, it was really unstable, holding a hand above transmitter shifted the frequency by 5Mhz. But still I was not dissapointed, great project!

C2 is 10p and not 10nC3 is 15p and not 15n The battery symbol is up-side-downYou don't have any capacitor across the battery. Should be 22nThe 4k7 should be 10k to 22k The circuit has too much inductance and too little capacitance in the tank circuit. The inductance should be 5 or 6 turns and the capacitance should be 47p. See properly designed BUG circuits on Talking Electronics.com website.